Sulfur-containing carboxylic acid esters



United States Patent O US. Cl. 260-481 8 Claims ABSTRACT OF THEDISCLOSURE Novel sulfur-containing ester compounds are formed byreacting a sulfur-containing carboxylic acid with an alcohol derivedfrom a resin acid, e.g., tetrahydroabietyl alcohol, dihydroabietylalcohol, dehydroabietyl alcohol, tetrahydroprimaric alcohol,dehydroprimaric alcohol, and mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of Ser. No. 343,492 filed Feb. 10, 1964, entitledOxidation Inhibitor, now abandoned.

BACKGROUND OF THE INVENTION In the stabilization of polyolefins, such ashigh molecular weight polypropylene, many problems have been encounteredin stabilizing the polyolefins so that the polyolefin may have a widerange of applications. One of the major problems which presentlycon-fronts those skilled in the art is to find stabilizer system whichnot only are useful to prevent oxidative degradation but preventoxidative degradation under a wide range of operating conditions. In thepast the most effective stabilizer systems for polyolefins have beenfound to contain compounds which were volatile and incompatible with thepolyolefin. In fact, the volatility and incompatibility were a definitelimit to the effectiveness of the stabilizer systems.

SUMMARY OF THE INVENTION The present invention is directed to new highmolecular weight esters which are useful in a costabilizer system forpolyolefins. More particularly, the invention is concerned withcompositions of matter which when used with a hindered phenol produce asynergistic effect in stabilizing polyolefins against oxidativedegradation. In its more specific aspects, the invention is concernedwith several new sulfur-containing ester compounds which are useful asco-stabilizers with a hindered phenol when incorporated in solidpolyolefins.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The esters of the presentinvention are formed from the reaction of a sulfur-containing carboxylicacid and a cyclic terpene alcohol or a hydrogenated derivative of acyclic terpene alcohol. The esterification is carried out in the usualmanner wherein the acid and alcohol are mixed or dissolved in a suitablesolvent with a catalytic amount of a mineral acid, and the water formedin the reaction is removed by suitable means. Preferred solvents for theesterification are aromatic compounds such as benzene, toluene orxylene. The mineral acids commonly used are hydrochloric, sulfuric andtoluene sulfonic acid. The mix- 3,494,947 Patented Feb. 10, 1970 'icevention are preferably the thiodialkanoic acids or alkylmercaptoalkanoic acids having the following structures:

RS--R where R is CH (CH COOH, R is -CH (CH COOH, or alkyl and n is l to5.

Specific acids suitable in the present invention are thiodipropionicacid, thiodibutyric acid, thiodihexanoic acid, hexadecylmercaptopropionic acid, octadecyl mercaptobutyric acid, ethylmercaptohexanoic acid, and lauryl mercaptobutyric acid. Also acids ofthe following formulae may be used:

HOOCCH (CH SS (CH CH COOH II HO 0 o omxomnswmnomo 0 OH 71:1 5 m =l to 16The alcohols used to form the esters of the present invention are cyclicterpene alcohols or the hydrogenated derivatives of cyclic terpenealcohols, and preferably are abietyl alcohols and isomers thereof havingthe following formulae:

CH OHQOH CH3 CH OH J-GHWHQ; CH(CH3)Q CH3 CH3 tetrahydroabietyldlhydroabietyl alcohol alcohol 0 H3 C H3O H CH a) 2 dehydroabietylalcohol CH CHzOH CH CHZOH C k/ C H C 2 5 OH3 C H3 CH3 CH3 DihydropimaricTetrahydropimaric alcohol alcohol The term abietyl alcohol is definedand used herein to mean the alcohols derived from abietic acid and allthe isomers thereof which includes all of the foregoing formulae as wellas mixtures thereof. The term abietyl group is used herein to mean thegroup derived from the abietyl alcohols. Other suitable alcohols arebicyclic monoterpenes such as borneol and the monocyclic monoterpenesillustrated by a-terpineol, fi-terpineol, y-terpineol and menthol. Alsosuitable as alcohols for preparing the esters of the present inventionare the hydrogenated cyclic terpene alcohols which are saturated. Thus,dihydroabietyl alcohol and dehydroabietyl alcohol may be hydrogenated toform tetrahydroabietyl alcohol, dehydropimaric alcohol may behydrogenated to form tetrahydropimaric alcohol, and a-terpineol,fl-terpineol, and 'y-terpineol when hydrogenated form the correspondingsaturated dihydroterpineol.

In the preparation of esters of the present invention for use as acostabilizer in polyolefins, a mixture of esters as well as a singleester may be formed. Thus, a mixture of the sulfur-containing carboxylicacids may be used or a mixture of cyclic terpene alcohols or a mixtureof both acids and alcohols. A particularly suitable costabilizer isprepared when a mixture of tetrahydroabietyl alcohol, dihydroabietylalcohol and dehydroabietyl alcohol is used to form mixed esters.

The polyolefln polymers treated in accordance with the present inventionmay be suitably exemplified by polyethylene, polypropylene,ethylene-propylene copolymers, ethylene-butene-l copolymers,ethylene-pentene-l copolymers, and the like, and are preferably solidpolymers having molecular weights in the range from about 10,000 toabout 1,000,000. These solid polymers may be produced by thepolymerization of the corresponding olefins employing the Ziegler-typepolymerization catalyst in a manner Well known to the art.

The phenolic portion of the new stabilizer system of the presentinvention is a hindered phenol. The term hindered phenol is defined as aphenol having at least one C; or greater tertiary alkyl group in theposition ortho to the hydroxy group. The hindered phenols may besuitably exemplified by 2,6-di-t-butyl-4-methylphenol; 2-t-butylphenol;4,4-butylidenebis(3-methyl-6 t butylphenol);2,2'-methylenebis(4-methyl-6-t-butylphenol); 4,4'-methylenebis(2,6-di-t-butylphenol); 4,4 (1,1butylidenebis(3-methyl-6-t-butylphenol) (1 ,06 bis(3-t-butyl-5-methyl-2-hydroxyphenyl)-mesitol; 4,4 thiobis(2-methyl- 6-t-butylphenol);and the like.

The preparation of the esters of the present invention is illustrated bythe following examples which are merely illustrative since the othercyclic terpene alcohols and sulfur-containing carboxylic acids will formesters in substantially the same manner.

Example 1 A mixture of tetrahydroabietyl alcohol, dihydroabietyl alcoholand dehydroabietyl alcohol (350 g.) and 0.5 mol (89 g.) ofthiodipropionic acid are dissolved in one liter of benzene in a flaskequipped with magnetic stirring and a Water separator. Five drops ofconcentrated sulfuric acid are added, and the mixture heated to refluxand refluxed for three days while collecting 17.2 g. of water. Themixture is cooled to room temperature and then the benzene removed on aRinco rotating evaporator. The resulting product is dissolved in ether,washed with three portions of water, dried over Drierite and the etherremoved on a Rinco rotating evaporator. The desired product, a mixtureof esters, 369 g., is recovered as a colorless, very viscous liquid. Theester structures are confirmed by NMR and IR analyses. Found: C, 77.22%;H, 10.63%; 0, 8.66%; and S, 4.40%. The foregoing analysis shows that themixture of esters is formed.

Example 2 A mixture of the tetrahydroabietyl alcohol, dihydroabietylalcohol and tetrahydroabietyl alcohol is dissolved in ether, Raneynickel added, and then hydrogen is Passed in until all the startingmaterial is converted to the tetrahydroabietyl alcohol. The solution isfiltered and the ether removed on a Rinco rotating evaporator to recoverthe. tetrahydroabietyl alcohol.

4 Example 3 Tetrahydroabietyl alcohol (292 g., 1.0 mol) obtained fromExample 2 and thiodipropionic acid (89 g., 0.5 mol) are dissolved in oneliter of benzene in a flask equipped with magnetic stirring and a waterseparator. Two drops of concentrated sulfuric acid are added, and themixture heated to reflux and refluxed for two days while collectingwater. The mixture is cooled to room temperature and then the benzeneremoved on a Rinco rotating evaporator. The last traces of benzene areremoved with heat lamps. There is obtained a colorless, very viscousliquid which is shown by analyses to be ditetrahydroabietylthiodipropionate.

Example 4 A mixture of dihydropimaric alcohol and tetrahydropimaricalcohol is admixed with thiodipropionic acid in a flask equipped with amagnetic stirring device and a water separator. Concentrated sulfuricacid is added and the mixture is heated to reflux While collecting theequivalent amount of water. The resulting product is worked up similarlyas in Example 1 and the product is a mixture of esters.

Example 5 A mixture of dihydropimaric alcohol and tetrahydropimaricalcohol is dissolved in ether, Raney nickel added. and then hydrogen ispassed through the mixture until all of the mixture is converted to thetetrahydropimaric alcohol. The solution is filtered and the etherremoved to recover the tetrahydropimaric alcohol.

Example 6 Tetrahydroabietyl alcohol and dithiodipropionic acid aredissolved in benzene, concentrated sulfuric acid is added, and themixture heated to reflux while collecting water in a Water separator.The product obtained after workup similarly in Example 1 isditetrahydroabietyldithiodipropionate.

Example 7 Tetrahydroabietyl alcohol and sulfoxydipropionic acid aredissolved in benzene, concentrated sulfuric acid is added, and themixture heated to reflux while collecting water in a water separator.The product obtained after workup similarly as in Example 1 isditetrahydroabietylsulfoxydipropionate.

Example 8 Tetrahydropimaric alcohol and 4,6-dithiaazelaic acid arerefluxed similarly as in Example 1 and the product obtained after workupis ditetrahydropimaric-4,6-dithiaazelate.

The esters formed are used in a stabilizer system and incorporated inpolyolefins in the amount from about 0.01 to about 1.5 percent by weightwith a preferred amount of about 0.1 to about 1.0 percent by weight. Theesters are incorporated in the polyolefins With a hindered phenol, andthe phenols are used in the amount from about 0.01 to about 1.5 percentby weight with a preferred amount from about 0.1 to about 0.7 percent byweight. The esters of the present invention and the hindered phenols maybe incorporated in the polyolefln by forming a solution thereof in asuitable solvent such as aromatic, paraflinic or naphthenic hydrocarbon.Suitable solvents may be illustrated by xylene, hexane or cyclohexaneand other members of these series. The synergistic mixture of thepresent invention may be sprayed over the pellets or particles of thepolyolefins, and the resulting mixture may then be extruded through asuitable extrusion device to cause the formation of the homogeneousmixture. The synergistic mixture may also be added to the polymerparticles without a solvent, and the resulting mixture subjected tomilling, extrusion or some other process to cause intimate mixture ofthe stabilizer system with the polymer composition.

The present invention will be further illustrated by the following datawhich are given by way of illustration and not by limitation from thescope of the present invention.

The compatibility of the stabilizer systems is tested usingpolypropylene and propylene-ethylene block copolymer as examples ofpolyolefins in forming compressionmolded plaques (4" x 4" x 75 mils).Samples are prepared of these polymers stabilized with the variousesters of the present invention as costabilizers with the hinderedphenols described above which form the synergistic stabilizer system.The plaques are allowed to stand at room temperature and are examinedperiodically for compatibility of the stabilizers. Those estercostabilizers which are not compatible with the polymer slowly exude tothe surface forming a dull film which is easily detected by visualobservation and which can be removed and identified by suitableanalytical tests. The test is usually carried out with dipinene-diphenolas the hindered phenol since it is completely compatible with thepolyolefins. It is found that the ester costabilizers of the presentinvention did not exude even after elght weeks as illustrated below:

exudes is totally unacceptable since a polyolefin would have a dull filmof the costabilizer on the surface. On the other hand, a costabilizerwhich is nonvolatile is necessary when the polyolefin is processed. Inthe extrusion of monofilament, processing temperatures are often usedwherein loss of costabilizer heretofore has occurred due to thevolatility of the costabilizer. Furthermore, there are many applicationsfor polyolefins wherein the operating conditions are such that anonvolatile stabilizing system is required. Thus, parts for the insideof dishwasher, driers, electrical equipment, etc. all require apolyolefin having a nonvolatile stabilizing system.

While the nonexuding and nonvolatile characteristics of the esters ofthe present invention have been emphasized to show their uniqueness,they are nevertheless etfective costabilizers with hindered phenols tostabilizer against oxidative degradation of the polyolefins. Thus, theesters of the present invention are as effective as costabilizers as thecostabilizers of the prior art.

The nature and objects of the present invention having been completelydescribed and illustrated and the best TABLE I Exudlng Wt. After AfterPolymer costabilizer percent 3 weeks 8 weeks Polypropylene Dilaurylthiodipropionate 1 0. 7 No No Do Dihexadecyl thiodipropionate 2 O. 7 NoNo Distearyl thiodipropionate 0. 7 Yes Yes Dibehenyl thiodipropionate 0.7 Yes Yes Product of Example 1 0. 7 No No Product of Example 3-- 0. 7 NoNo Dilauryl thiodipropiona 0. 7 No No Drhexadecyl thiodipropionate" 0. 7No No Distearyl thiodipropionate 0. 7 Yes Yes Dibehenyl thiodrproplonat0. 7 Yes Yes Product of Example 1 0. 7 No No Product of Example 3- 0. 7No No 1(C12H350OCCHQCHQMS (CmH33OOCCHgCHahS. (C1gH37OOCCHgCH hS.(CMHlsOOCCHaC G028 By another test, the volatility of the stabilizersystems is determined by aging polypropylene samples, formed bycompression molding with the stabilizer system incorporated in thepolypropylene, in a forced air circulating oven at 280 F. The samplesare formed as pads of about 1%." x /2" x 10 mils. Periodically, thesamples are removed from the oven and analyzed for ester costabilizercontent. The esters of the present invention used as a costabilizer werefound to be nonvolatile as illustrated by the following data:

Table II Costabilizer: Percent present after 40 days Dilaurylthiodipropionate Failed in 18 days. Dilauryl thiodipropionate Failed indays. Distearyl thiodipropionate 60. Dibehenyl thiodipropionate 75.Product of Example 1 80. Product of Example 3 80.

1 Determined by absorbance/mil (IR).

From Table II, it is seen that dilauryl thiodipropionate and dihexadecylthiodipropionate are completely volatilized from the samples whensubjected to circulating air at 280 F. in less than days.

It is thus obvious from the foregoing that the esters of the presentinvention when used as costabilizers in polyolefins are both nonexudingand nonvolatile. These characteristics appear surprising since whencompared to the esters of a sulfur-containing carboxylic acid and analiphatic alcohol these two characteristics are not present in any oneester. It is emphasized that a costabilizer which mode thereof setforth, what we wish to claim as new and useful and secure by LettersPatent is:

1. A composition selected from the following general formulae:

ROOC (CH CH -S(CH S-CH (CH OOOR ROOC (CH CH S(CH S (CH CH 5. Acomposition according to claim 4 wherein R is the radical derived fromtetrahydroabietyl, dihydroabietyl and dehydroabietyl alcohols.

7 a 8 6. A composition according to claim 1 wherein said gen- ReferencesCited formula is UNITED STATES PATENTS ROOC CHZ CHZ S CH2 CHZ .COOR2,640,848 6/1953 Harman et a1 260-481 7. A composition according toclaim 6 wherein R is 5 LORRAINE WEINBERGER, Primary Examiner the radicalderived fromtetrahydroabictyl, dihydroabietyl E GLEIMAN, AssistantExaminer and dehydroa-bietyl alcohols.

8. A composition according to claim 6 wherein R is US. Cl. X.R. theradical derived from tetrahydroabietyl alcohol. 26045.85

